2. Technologies for RIFA Control in Taiwan temperature of Fig. 1 Areas commonly infested with RIFA (dark gray) and with sporadic occurrence (light gray) in Taiwan. H. LIN and C. LIN Taiwan, that overcame the difficulty of widely distributing control baits, reduced the labor cost resulting from the mega scale of RIFA monitoring programs, and raised awareness of the general public about ecological crises caused by invasive alien ants are focused on and discussed in the following sections. 2.1 Unconventional Methods against Single RIFA Nests - Liquid Nitrogen Freezing, Hot Water Vapor Steaming and Dry Ice Treatment When RIFA was discovered on the busy streets of a city in Taiwan, the damage it causes and its ferocious aggression quickly caused a great panic among the residents. Large amounts of liquid insecticide were applied on RIFA nests and these soon wiped out most of the worker ants. This seemed to be favored by the locals, who hoped quickly to eradicate RIFA. However, it also drew much attention from the general public regarding the pollution and hazards of the massive use of the pesticide involved. Therefore, liquid nitrogen freezing, hot water vapor steaming and dry ice treatment for single mounds were developed as cleaner alternatives, and have been put into practice in the government sector and private companies. Liquid nitrogen quickly cools the target to −196°C and then vaporizes into harmless nitrogen gas before dissipating. When liquid nitrogen is injected into a RIFA mound until it is full, the whole mound as well as most of the ants inside are soon frozen and killed (Fig. 2), resulting in about 90% of mortality of the nest (Fig. 3) ( Lin et al., 2013). Hot water vapor steaming was employed with several injections of pressurized vapor (95°C–100°C, 7 kg/cm2) inside and around ant mound (Figs. 4 and 5), which raised the temperature to over 80°C at a distance of 25 cm from the center of the mound, and then drenching the area with hot water. (APHIA, 2023). The mortality rate in these nests was about 80%–95%. Fig. 2 Liquid nitrogen is injected into RIFA nests through metal pipes. Frost is observed inside and outside the treated the nest, treatment. the cryogenic indicating Currently, the RIFA population has been effectively restrained in the northern part of Taiwan thanks to persistent control efforts from 2004 (Yang, C.C.S et al., 2009; Liu, H.K. et al., 2020.; Liu, Y.S et al., 2021). The most serious areas with common occurrence of RIFA are located in Taoyuan City, New Taipei City, Hsinchu County and Kinmen County, while those where RIFA has occured sporadically are: Taipei City, Keelung City, Hsinchu City, Miaoli County, Taichung City, Yilan County, Hualien County and Lianjiang County (Fig. 1) (APHIA, 2024) There are four common ways to monitor RIFA in Taiwan: visual inspection, fall traps, bait traps and detection using RIFA detection dogs. Bait trapping is the most widely adapted method while others were also used in accordance with the situation and purposes of the investigation. Periodic area-wide sprinkling of toxic control baits has been the recommended way to manage RIFA over large areas. Contact insecticide injections were the most frequent treatment against single ant mounds, while unconventional non-pesticide approaches, like liquid nitrogen injection, hot water vapor steaming or dry ice were also developed and put into practice. Some of these measures can be found in “Effectiveness Evaluation Procedures of Detection, Monitoring and Control against Red Imported Fire Ants” from the “Standard Operating Procedures for Fire Ant Control” (APHIA, 2023). The unique and effective techniques developed in 144 set up to assist with various prevention and control matters, and formulate “Standard Operating Procedures for Fire Ant Control” (APHIA, 2023). The average central and local government have jointly provided hundreds of millions of TW$ in funding per year to remove RIFA from Taiwan and relieve concerns among the general public. After 20 years of fighting against RIFA, the investment has accumulated to roughly 3 billion TW$.
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